The present invention relates to a motor control device having a control component for making available a control signal. Furthermore, the present invention relates to a corresponding control method.
The speed control or rotational speed control and also the position control of drives is frequently adversely affected by noise and other interference variables. This problem is explained in more detail with reference to the speed control circuit for linear drives which is illustrated in FIG. 1. A reference speed vref is predefined for the control circuit. In an adder Sum1, an actual speed vist is subtracted from this reference speed vref so that a difference or differential signal ev is obtained. The differential signal ev is amplified proportionally with the gain factor Kp in an amplifier G1. In the amplifier G2, integrator I1 and adder Sum2 which are connected downstream, an I component with an adjustment time Tn is taken into account. A current i which results from the adder Sum2 is converted into a linear position x by a motor M which constitutes the controlled system. Here, the motor M is modeled by an amplifier G3 and two integrators a2v and v2x connected downstream. The amplifier G3 converts the current i into an acceleration a in accordance with a force constant KF. Said acceleration a is converted in the first integrator a2v into a speed v and subsequently into a position x in the second integrator v2x. 
A signal transmitter G taps the position x, an interference signal rx being unintentionally added to the position signal x, which is indicated by the adder Sum3. The interference signal rx is produced, for example, by quantization noise or other noise and other interference variables. The signal transmitter G thus supplies an actual position signal xist.
The signal transmitter evaluation unit A in the feedback branch serves to convert the actual position signal xist into the actual speed signal vist. To do this, differentiation which is discrete over time is carried out with the delay element D1, the adder Sum4 and the amplifier G4. The blocks D1, Sum4, G4, vref, Sum1, G1, G2, I1, Sum2 usually operate in this context in a discrete fashion overtime, the clock rate corresponding to the delay T of the delay element D1. Correspondingly, the actual position signal xist is not continuous either but rather is sensed in a discrete fashion over time with this clock rate. To this extent, the signal transmitter evaluation A forms the difference between the current and preceding actual positions which is weighted with a factor (the factor here is 1/T here).
The aim is usually to obtain the highest possible dynamics. i.e. (1) the speed v responds to changes in the reference speed vref as quickly as possible, and (2) sudden interference forces which in FIG. 1 would correspond to an additional additive component in the acceleration a which is not indicated there are as far as possible only to have a brief effect on the speed v. In order to obtain the highest possible dynamics, the aim is to implement the highest possible values for Kp in the amplifier G1 and 1/Tn in the amplifier G2 of the controller R. However, in practice there are limits on this, inter alia because the interference variable rx falsifies the actual value vist of the rotational speed. That is to say even if the true speed v corresponds to the reference value vref, the actual value vist which is determined generally differs from vref, which, when Kp is too high, gives rise to excessive motor currents i and, consequently, leads both to additional heating and generation of noise and also to excessive acceleration values a and also to the speed value v deviating from the reference value vref. In this way, even when vref is constant, an undesired additional noise-like variation occurs both in the current i and in the speed v. In the case of the current i, this variation is referred to as current ripple, and in the case of the speed v it is referred to as speed ripple.
The objective is then to carry out a modification to the effect that current ripple and speed ripple can be reduced for given dynamics and conversely the control can be made more dynamic (by increasing Kp and, if appropriate, 1/rn) without at the same time increasing the current ripple and the speed ripple.
A known modification of the control circuit illustrated in FIG. 1 comprises filtering the actual value of the speed according to FIG. 2. Here, the actual value of the speed vist is smoothed by a low pass filter TP before it is fed into the adder Sum1. However, a disadvantage of this solution is that the low pass filter TP limits the achievable dynamics.
A further possible way of minimizing the current ripple and the speed ripple is to reduce the interference signal rx. For example a higher resolution signal transmitter for the position x is suitable for this. The higher resolution signal transmitter permits the quantization noise to be reduced. The disadvantage of a signal transmitter with higher resolution is however the higher costs.
Furthermore, the interference signal rx can be reduced, for example, by oversampling, as has been described in the paper by Roland Kirchberger “Verbesserte Erfassung von Lage und Geschwindigkeit an Hochgeschwindigkeitsspindeln” (Improved sensing of position and speed on high speed spindles]”, Lageregelseminar [Position control seminar] 2001, 26-27, Oct. 2001, Stuttgart. However, the greater degree of expenditure on hardware and the delay in the actual value of the speed vist compared to the true value v are disadvantageous here.
Using an additional acceleration sensor as is provided in the document DE 100 24 394 A1 allows the adverse effects of the interference variable rx on the actual speed vist and thus on the current ripple and the speed ripple to be likewise reduced. However, the additional expenditure on the acceleration sensor and its evaluation are disadvantageous here.